June July Aug Sept Oc1 



Fire Se Q son 



Figure 10. — Calculated heat content trends. 



CONCLUSIONS 



This study shows the following relation- 

 ships for chamise: 



1 . The ether extractive content of the 

 leaves ranged from a low of about 8.5 percent 

 in the spring to about 12 percent in the fall 

 for leaves and from 4.3 percent (spring) to 8.9 

 percent (fall) for stems. The dip at spring is 

 probably partly due to new leaf flush and 

 stem elongation. This new plant material has a 

 lower extractive content. 



2 . The heat content of the total fuel, 

 leaves, and small stems is directly related to 

 their ether extractive content. The heat con- 

 tent of leaves increased 600 B.t.u./lb. and that 

 of stems increased 465 B.t.u./lb. from May to 

 October. 



3. The heat content of the leaves and 

 stems after extraction increased during the 

 same period. Increase for leaves was about 

 171 B.t.u./lb.; and for stems, about 148 

 B.t.u./lb. 



4. The computed heat content of the 

 ether extractives was much higher from the 



stems and varied with time of year. It was at 

 its highest for leaves at the end of the fire sea- 

 son. Values as high as 17,378 B.t.u./lb. for 

 leaves and 24,533 B.t.u./lb. for stems were 

 found. This vsiriation implies a significant 

 compositional change with season in the com- 

 pounds making up the extractives. 



The change in heat content of the leaves 

 during the fire season (June through October) 

 can be summarized graphically using the equa- 

 tions and data from this study (fig. 10). 



The effect of this change will not be known 

 until further research establishes the relation 

 between flammability and extractives. An in- 

 crease in flammability would be expected be- 

 cause of the increase in heat content. We 

 found a direct relation between extractive con- 

 tent and the burning rate of aspen leaves 

 (Philpot 1969). Also, if part of the extractives 

 added to the leaves is deposited on the surface, 

 rate of spread may be enhanced. However, the 

 change probably is not very important from a 

 fire hazard standpoint if the added heat con- 

 tent is not more available than the rest of the 

 fuel within a specific species. 



9 



